Since all three countries have takings, or partial takings, written into law in the form social welfare, labor, and environmental law and exist in the form of legislated, judiciated, and administrative(regulatory)law, NAFTA was written to supercede all these laws. Thus, if MetalClad takes hit in Mexico over enviro laws,it is a taking and they can/did win a settlement from the NAFTA arbitration panel. If Canada tries to force a US tobacco company into a certain type package label, it is a taking. Same with trucking. The US's refusal to admit mexican trucks is a taking and the fine set by the arbitration panel is $2 billion/year.
If this same protection from takings is written into the future trade areements in South America and the Caribbean, then there becomes two sets of laws: intranational and international. Those operating under the intranational set are at extreme disadvantage to those operating under the international set.
At this point SCOTUS would step in and declare every social, labor, and environmental law written in the last 100 years to be unconstitutional.
Libertarian Heaven on Earth.